Agricultural harvesters, such as agricultural combines, are designed to travel through agricultural fields harvesting crops. Agricultural combines receive crop severed from the ground and convey it to threshing, separating and cleaning devices within the agricultural combine. In a typical arrangement, the agricultural harvesting head severs the crop from the ground and conveys it to the central region of the harvesting head where it is then conveyed rearward into a central and forwardly opening aperture in the front of the agricultural combine proper.
Agricultural harvesting heads are quite long, on the order of 10-15 m in overall length. In order to accurately follow the contours of the ground and sever crop at the appropriate point on the stem, agricultural harvesting heads have been made in sections that are generally hinged with respect to each other. A typical agricultural harvesting head of this type is formed in two or three sections that are pivotable with respect to each other. They pivot with respect to each other about a generally horizontal and fore-and-aft extending axis. Thus, a two section agricultural harvesting head would have one pivot axis, and a three-section agricultural harvesting head would have two pivot axes.
To better follow the contours of the ground, the agricultural harvesting head is mounted to the front of the feederhouse such that it can move with respect to the feeder house.
In one arrangement (U.S. Pat. No. 6,675,568 B2) the agricultural harvesting head is a draper head having three frame sections (a center section, a left-wing section and a right wing section). In this arrangement each of the wing sections are hinged with respect to the center section about two pivot joints with pivot pins (see: FIG. 6, items 17H, 27; FIG. 20, items 71A, 71B). The pivot joints permit the left wing section and the right wing section to pivot up and down with respect to the center frame section and thereby follow the contours of the ground.
In addition to that contour-following capability, the center frame section is mounted on an “adapter” that is fixed to the front of the feederhouse. This adapter permits the center frame section to move up and down with respect to the front of the feederhouse. It also permits the wing sections to move up and down with respect to the front of the feederhouse, since they are attached to and supported on the center frame section.
A spring-loaded support assembly is coupled between the adapter frame and the center frame section to hold the center frame section up in the air at an optimum cutting height with respect to the adapter. As the ground moves up and down, the spring-loaded support assembly provides a lifting force to transfer the weight to the feederhouse of the combine. Unfortunately, this lifting force varies depending on the position of the center section with respect to the feederhouse. The lower the center frame section is with respect to the adapter and the feederhouse, the more weight is transferred to the adapter and feederhouse and the smaller the force applied to the ground. The higher the center frame section is with respect to the adapter and the feederhouse, the smaller the weight is transferred to the adapter and feederhouse and the more weight is applied to the ground.